JPS6058298A - Anaerobic digestion treatment - Google Patents

Abstract

PURPOSE:To contrive to accelerate sludge reaction speed in anaerobic digestion treatment by removing a bad influence due to a minute amount of oxygenm by adding a carrier preliminarily deoxygenated to a digestion tank to perform anaerobic digestion treatment. CONSTITUTION:In an anaerobic digestion treatment method wherein a carrier such as activated carbon is added to enhance the reaction speed of sludge, the above-mentioned carrier is preliminarily deoxygenated by 90% or more while the treated carrier is added to a digestion tank and a bad influence due to a minute amount of oxygen adsorbed with the carrier is prevented to enhance reaction accelerating effect due to the carrier. By this method, the number of days stayed in the digestion tank are shortened and good treatment is enabled even if the amount of a charged org. substance is excessive load.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an anaerobic digestion treatment method, and relates to an improvement in a reaction promotion method thereof.

[Technical background of the invention and its problems]

Anaerobic digestion is widely used as a method for treating organic wastes such as urine or sewage sludge generated at sewage treatment plants.

In the anaerobic digestion method, high-molecular organic substances such as carbohydrates, fats, and proteins in organic waste are first reduced to low molecules by acid-producing bacteria, which are facultative anaerobes. Then, by a certain methane bacteria,
Fatty acids are decomposed into methane, carbon dioxide, etc.

This type of anaerobic digestion method is more efficient than aerobic treatment.
Since no 13111 air is required, there are advantages such as low running costs, (11) less sludge generation, and the ability to effectively use the generated methane as an energy source. On the other hand, it has the disadvantage that the reaction rate is very slow and the residence time in the digester requires 20 to 30 days, so a large-capacity digester is required.

As a method to overcome these drawbacks, a method is known in which a carrier such as activated carbon zeolite or vermiculite is added to the digestion tank to increase the reaction rate. It is believed that the reason why these carriers act as reaction accelerators is that the density of bacterial cells is increased by attaching the aforementioned acid-producing bacteria and methane bacteria to these carriers.

However, the effect of promoting the reaction by these conventional methods is not sufficient, and a method that provides a greater effect of promoting the reaction has been sought.

According to research by the inventors, the main reason why these conventional methods were not able to obtain a sufficient reaction promotion effect was that oxygen adsorbed on the added carrier adversely affected the digestion reaction. found.

That is, the above results were confirmed by the following three experiments.

The first experiment used two small digesters #J with an effective volume of 10 liters (IJ liters) to homogenize equal amounts of raw sludge obtained from a sewage treatment plant and seed sludge (digested sludge pulled out from the digester). 11. from each small digester at a predetermined time every day. A long-term digestion experiment was conducted in which 1 liter of raw material sludge was added at the same time, and no reaction accelerator such as activated carbon was added.

The two small-sized digesters mentioned above have exactly the same dimensions, are stirred at the same speed, and are installed in the same constant-temperature water tank to ensure the same digestion temperature. All conditions are the same.

The amount of digestive gas generated was measured using a wet gas meter, and the measured values were output to a printer every hour.

The measurement results of the amount of digestive gas generated from these two small digesters are shown by solid lines and broken lines as measured values up to the fourth day in FIG.

As mentioned above, since the experiment east 1't= is the same, 2
The amount of digestive gas generated from the two digesters should be the same. However, as is clear from FIG. 1, the times at which the peak of the amount of digestive gas produced were different, and the cumulative value of the amount of digestive gas produced per day was also quite different, with one being about twice as much as the other. A similar experiment was conducted again, but the results were similar to the previous one.

The reason for this difference in the amount of digestive gas produced was thought to be due to the influence of oxygen. This is because when the digested sludge is pulled out from the digester every day, negative pressure is created in the digester, so at this time the atmosphere (
I thought it might have been contaminated with oxygen. In fact, the experimental equipment at this time had a structure in which the sample outlet side of the wet gas meter was left open to the atmosphere, allowing air to enter from there. Approximately 11 atmospheres are thought to have been mixed in when the digested sludge was extracted from both digesters, but the water surface conditions of the digested sludge (scum generation, etc.) were different, so the rate of oxygen dissolution into the liquid phase was affected. It was thought that the degree of adverse effects of dissolved oxygen on acid-producing bacteria and methane bacteria varied.

Therefore, the following second experiment was conducted. That is,
The second experiment was carried out in the middle of the first experiment by attaching a 201 Tetra Bag (a bag used for odor sampling, etc.) filled with nitrogen gas to the sample outlet side of the wet gas meter. The flow was reversed to prevent air from getting mixed in. The measurement results of the amount of digestive gas generated in the second experiment are shown as the measured values from day 4 onward in FIG. As is clear from FIG. 1, as a result of preventing the mixing of oxygen, the amount of digestive gas generated increased in both digesters, and the values remained at the same level without any difference. As a result, it was found that the trace amount of oxygen gas mixed in reduced the efficiency of digestion.

In other words, when the digested sludge is pulled out, a small amount of air is mixed in, but when the raw sludge is then put in, a mixture of air and digestive gas is expelled, and the generated digestive gas also causes damage to the digestion tank. The gas at the top is replaced, so
This is because although the amount of oxygen dissolved in the liquid phase was estimated to be small, it adversely affected one reaction.

[Purpose of the invention]

An object of the present invention is to provide an anaerobic digestion method that eliminates the adverse effects of trace oxygen and enhances the reaction promoting effect of a carrier.

(Summary of the Invention) The present invention relates to an anaerobic digestion method for increasing the reaction rate of sludge by adding a carrier.
By deoxidizing % or more of oxygen and adding it to the digestion tank, the adverse effect of oxygen adsorbed on the carrier is prevented and the reaction promotion effect is enhanced.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below. In the present invention, activated carbon, zeolite, vermiculite, etc. are used as the carrier added to the digestion tank for reaction promotion. This is deoxidized in advance by about 90 g or more, and the deoxidized amount is added into the digestion tank.

In the case of digestion using a deoxygenated carrier,
The content of the experiment will be explained. This third experiment has an effective volume x
A batch experiment was conducted under the conditions shown in Table 1 using three of the above-mentioned small-sized digesters. Here, a batch experiment is an experiment in which a predetermined amount of raw material sludge and seed sludge are sealed in the digestion tank at the start of the experiment, and then no sludge is introduced or withdrawn.

For the NOI digestion tank, activated carbon that had been left in a constant temperature bath at about 100 °C for 3 hours to desorb the adsorbed oxygen was used as a carrier, and for the NO2 digestion tank, activated carbon that had been left indoors as a carrier was used. and no carrier was added to digester NO3.

Figure 2 shows slight changes in the generation of iN gas from the digested 1NO1-NO3 over time. As is clear from the figure, as shown by curve a, in the digestion 4i+fNOx with the addition of activated carbon that desorbs oxygen, the digestion gas generation rate is lower than that of the conventional method (curve mb) in the digestion tank NO2. It was found that the reaction acceleration effect becomes larger (for example, it is about 1.5 times larger when compared after 200 hours of digestion reaction time), and the reaction promotion effect becomes larger.

In these experiments as well, the amount of digestive gas generated was measured using a wet gas meter and output to a printer every hour. In addition, the activated carbon used was "Shirasagi A" manufactured by Kyushu Yakuhin Co., Ltd.

A method of decomposing oxygen gas adsorbed on activated carbon, which is a reaction accelerator, by taking out digestion gas from a digestion gas storage tank, purging the carrier, and decomposing the adsorbed oxygen into methane, the main component of digestion gas. The carrier is heated to 70 to 100'O by using a method of replacing carbon dioxide gas, a heat medium such as steam or hot water used to heat the digestion tank, or engine waste heat of the digestion gas power generation system, and then heated for several hours. An effective method is to leave it alone. Heat carrier engine waste heat such as digestion gas, steam, and hot water is inevitably obtained in anaerobic digestion processes and digestion gas power generation systems, so it has the advantage that the cost required for oxygen desorption is low. . However, the present invention is not limited to the method of desorption and decomposition of oxygen adsorbed on the reaction accelerator.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to further increase the reaction rate than before, so the residence time in the digester can be reduced, and even when the amount of input organic matter is overloaded, good treatment is possible. becomes.

[Brief explanation of the drawing]

FIG. 1 is a graph showing experimental results explaining the state of generation of digestive gas in a general anaerobic digestion process, and FIG. 2 is a graph showing experimental results explaining the present invention in detail.

Claims (1)

[Claims] An anaerobic digestion method that increases the reaction rate of sludge by adding a carrier, characterized in that the carrier is deoxidized by 90% or more in advance and then added to a digestion tank.